<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>vw布局</title>
</head>
<body>
    <div class="parent">
        <div class="son"></div>

    </div>
</body>

<style>
    body{
        margin: 0;
    }
    .parent{
        width: 80vw;
        height: 300px;
        background-color: aliceblue;
    }

    .son{
        width: 20vw;
        height: 300px;
        background-color: black;
    }
    /* 在500px的屏幕上 son 宽度是  */
</style>
</html>